Internet Engineering Task Force L. Song
Internet-Draft Beijing Internet Institute
Intended status: Experimental P. Vixie
Expires: January 3, 2019 TISF
S. Kerr
July 2, 2018
An Proxy Use Case of DNS over HTTPS
draft-ietf-dnsop-dns-wireformat-http-03
Abstract
This memo introduces a DNS proxy use case to tunnel DNS query and
response using DNS over HTTPs (DOH) protocol, a newly proposed DNS
transport. The proxy use case is useful as a incremental adoption
tool when DOH is not widely available in old-transport client and
server.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Use case description . . . . . . . . . . . . . . . . . . . . 3
3. Original transport indicator in DOH proxy . . . . . . . . . . 4
4. Implementation considerations . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
RFC 1035 [RFC1035] specifies the wire format for DNS messages. It
also specifies DNS transport on UDP and TCP on port 53, which is
still used today. To enhance the availability of honest DNS, a new
DNS transport: DNS over HTTPs (DOH) [I-D.ietf-doh-dns-over-https] is
proposed which transport DNS over HTTPs , in a way to cure DNS's
long-time suffering from on-path attack by spoofing and blocking.
This memo introduces a DNS proxy use case to leverage the DOH
protocol as a substrate to tunnel DNS data over HTTPs which is called
DOH proxy in the rest of the document. It is useful especially when
most DNS stub-resolvers and far-end servers are not aware the new DOH
protocol, but a public or private proxy using DOH can be deployed and
offer DOH capacity to users to bypass the networks where DNS is not
working properly.
Just as a normal DNS proxy described in [RFC5625], DOH proxy works as
a simple DNS forwarder keeping the transparency principle, so any
"hop-by-hop" mechanisms or newly introduced protocol extensions
operate as if the proxy were not there.
In order to keep the transparency of DOH proxy, a new variable
"proto" in URI Template is defined for DOH proxy use case. It allows
the proxy server use the same transport protocol (UDP or TCP) to
forward DNS query to far-end server just as the stub-client does
without DOH proxy.
May REMOVE BEFORE PUBLICATION: Comparing using a general VPN, the DOH
proxy can work on an actual HTTP server, so it can be hosted on a
machine that also serves web pages. This means that DNS over HTTP is
slightly more "stealthy" than a VPN, in that it can be
indistinguishable from normal web traffic.
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2. Use case description
The typical scenario is that a DOH proxy sitting between stub-
resolver and the recursive server. The stub-resolver is configured
sending DNS query to a DOH proxy and expects reply from the same DOH
proxy . Just as a normal DNS proxy described in [RFC5625], DOH proxy
works as a simple DNS forwarder keeping the transparency principle.
The only difference is DOH proxy consist two part, a proxy client as
a initiator of DOH tunnel and a proxy server as a terminator. The
proxy client speaks DOH with proxy server carrying the same DNS query
received from stub-resolver.The proxy server will forward the exact
DNS query received from stub-resolver to the configued recursive
server.
To keep the transparency principle of DOH proxy, any "hop-by-hop"
mechanisms or newly introduced protocol extensions operate as if the
DOH proxy were not there. Different from the native DOH protocol, in
DOH proxy use case, there should be a indication introduced for proxy
client to tell the proxy server original transport (UDP or TCP) the
stub-resolver uses to send DNS query to proxy client.
For example if the proxy client receives the query via UDP, then it
will notify the proxy server with a "proto=udp" indicator which is
defined in Section 3. If proxy client receives the query via TCP,
then it will carry a "proto=tcp" indicator with the same DNS query
without the two-byte length field defined in DNS over TCP [section
4.2.2 in [RFC1035]].
Besides the original transport indicator, as specified in DOH
document, the proxy server MUST be able to process both "application/
dns-message"request messages and forward the query to a configured
recursive server using the same transport between sub-resolver and
proxy client. The response will be delivered back to sub-resolver
accordingly. In DOH proxy use case, each DNS query-response pair is
mapped into a DOH query-response pair. And the transport for DNS
query and response MUST be the same.
It is possible that a proxy client as a module can be deployed in the
same host with the sub-client listening to a loop-back address. A
proxy server can be implemented that way to host a recursive DNS
process as well. The can be combined to form four deployment
scenarios of DOH proxy use case.
It is also possible to use the proxy server as a regular web server
at the same time that is acting as a proxy server.
Note that the proxy client will face the same bootstrapping problem
described in DOH when the HTTPs request needs to resolve the name of
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server and send the request to on IP address. The strategy is either
use the IP directly or use another resolver (like the normal DHCP-
supplied resolver) to lookup the IP of the server.
3. Original transport indicator in DOH proxy
In DOH document[I-D.ietf-doh-dns-over-https], the HTTP request uses a
URI defined by the DOH server through the use of a URI Template in
which no variables is defined. In this document, a new variable
"proto" is defined as the indicator of original transport. For
example, The URI "https://example.com/proxy_dns?proto=tcp" will cause
the server to make a request using TCP. And the URL
"https://example.com/proxy_dns?proto=udp" will cause the server to
make a request using UDP.
4. Implementation considerations
The DOH proxy may return TC bit to the sub-resolver which will cause
TCP fallback starting from the sub-resolver. An alternative advised
is that the proxy has to have sufficient smarts to recognize the
returned TC bit and re-issue the request over TCP to the back-end DNS
server.
Another implementation is suggested that DOH proxy server has a pool
of TCP connections from the proxy to the back-end DNS server(s), over
which incoming requests can be multiplexed.
5. Security Considerations
The DOH proxy use case does not introduce new protocol and any new
security considerations since it is built on the DNS over HTTPS
protocols. All security considerations and recommendations apply in
DOH proxy use case.
Since DOH proxy is a also a special DNS proxy, the security
recommendations of DNS proxy RFC 5625 [RFC5625] also apply in DOH
proxy use case.
Note that the ability to perform DNS queries in this way may allow
users to bypass local DNS policy. This may be problematic in any
environment where administrators need to enforce specific DNS
behavior, such as an enterprise environment. The protocol outlined
here does not introduce any new capabilities in this area, but by
creating a more standardized way of doing this it may cause
operational problems for enterprise administrators.
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6. IANA considerations
No IANA considerations for DOH proxy
7. Acknowledgments
Thanks to Bob Harold, Paul Hoffman, Julian Reschke, Martin Thomson,
Tony Finch ,Ray Bellis and Erik Kline for their review and comments.
8. References
[I-D.ietf-doh-dns-over-https]
Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", draft-ietf-doh-dns-over-https-12 (work in
progress), June 2018.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, .
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, DOI 10.17487/RFC5625, August 2009,
.
Authors' Addresses
Linjian Song
Beijing Internet Institute
2nd Floor, Building 5, No.58 Jing Hai Wu Lu, BDA
Beijing 100176
P. R. China
Email: songlinjian@gmail.com
URI: http://www.biigroup.com/
Paul Vixie
TISF
11400 La Honda Road
Woodside, California 94062
US
Email: vixie@tisf.net
URI: http://www.redbarn.org/
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Shane Kerr
Antoon Coolenlaan 41
Uithoorn 1422 GN
NL
Email: shane@time-travellers.org
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